This invention relates to a television receiver of electronic tuning type.
In a television receiver of electronic tuning type, a local oscillator in its tuning circuit includes a variable capacitance diode, and a tuning voltage corresponding to a specific channel selected by a TV viewer is applied to this variable capacitance diode so that the tuning circuit can be tuned to the selected channel frequency. In the television receiver of this type, a plurality of digital data indicative of tuning voltage values corresponding to a plurality of channels respectively are stored previously in a tuning data memory, and a digital data corresponding to a specific channel selected by a TV viewer is read out from the memory to be subjected to D/A conversion in a D/A converter thereby providing an analog voltage or tuning voltage which is applied to the variable capacitance diode in the local oscillator of the tuning circuit.
However, the operating characteristic of the variable capacitance diode in the television receiver of this type tends to vary with time, due to, for example, a temperature drift and a secular variation. As a result of such a variation in the operating characteristic of the variable capacitance diode, a deviation of each individual optimum tuning point takes place for the tuning circuit with the corresponding tuning voltage data stored in the tuning data memory, and a clear picture will not be reproduced on the screen of the CRT.